Acoustic diode

Abstract

A sonic transmitter has placed in front of it or in its acoustic beam path, an acoustic diode comprising at least two peripherally secured foils in mutual contact, the foils having opposed surfaces with a degree of adhesion and/or cohesion such that they may be pulled apart beyond a threshold value which may be acted upon--of negative sound pressure thus suppressing negative sound pulses, whereas positive sound pressures may be transmitted at almost unaltered levels in view of the existing mechanical contact of the foils.

I claim: 
     
       1. Sonic transmitter comprising a source of sonic waves and a system for suppression of negative sound pulses, wherein there is positioned across the acoustic signal path of said sonic wave source an acoustic discriminator comprising at least two peripherally secured foils normally in contact with each other, said foils having opposed surfaces with a degree of cohesion between them such as to enable them to be pulled apart at a variable threshold value of negative sound pressure, thereby suppressing said negative pulses whereas positive sound pulses can be transmitted at almost unaltered levels in view of the existing mechanical contact of the foils. 
     
     
       2. A sonic transmitter as claimed in claim 1, wherein said cohesion between said foils is obtained by means of a substance interposed in gaps between the foils. 
     
     
       3. A sonic transmitter as claimed in claim 1, wherein said cohesion is obtained by means of a vacuum between said foils. 
     
     
       4. A sonic transmitter as claimed in claim 1, wherein said cohesion is obtained by electrostatic action between said foils. 
     
     
       5. A sonic transmitter as claimed in claim 1, wherein said foils comprising a material selected from metal and plastics material. 
     
     
       6. A sonic transmitter as claimed in claim 1, wherein more than two said foils are provided, at least one having a piezoelectric property. 
     
     
       7. A sonic transmitter as claimed in claim 1, wherein said opposed surfaces of said foils are roughened. 
     
     
       8. A sonic transmitter as claimed in claim 1, wherein the foil thickness is smaller than the wavelength of the sound waves emitted by said source. 
     
     
       9. A sonic transmitter as claimed in claim 3, wherein the static pressure between the foils is adjustable by means of a connectible vacuum pump. 
     
     
       10. A sonic transmitter as claimed in claim 1, wherein the foils of the acoustic diode have a curvature adapted to the sound wavefront emitted by said source. 
     
     
       11. A sonic transmitter as claimed in claim 1, wherein several acoustic diodes are placed laterally parallel to each other under mutual separation and are covered at the extremities by an envelope having gas-filled spaces with an easily adjustable negative pressure. 
     
     
       12. A sonic transmitter as claimed in claim 1, wherein said sonic wave source is a piezo-electric transducer which comprises a piezo-electric layer of cylindrical piezo-ceramic elements which are situated in a carrier in the form of spheroidal bowl which concentrates the ultrasonic oscillation on a focus, and wherein said acoustic discriminator is positioned across the acoustic signal path between said transducer and said focus.